Project Summary Our current approaches to the diagnosis and treatment of lymphoid malignancies do not reflect emerging data regarding pathogenetic mechanisms and associated rational treatment targets. For example, one of the main lymphoid malignancies to strike young and otherwise healthy adults, classical Hodgkin lymphoma (cHL), is largely defined by its morphologic appearance and treated with an empiric combination of available chemotherapeutic agents. We previously hypothesized that 9p24.1/PD-L1/PD-L2 copy number alteration (CNA) was a genetic mechanism of immune evasion in cHL and considered the PD-1 pathway to be a rational therapeutic target in this disease. After defining recurrent 9p24.1 copy gain and increased PD-L1/PD-L2 expression as high-frequency events in cHL, we explored the clinical activity of PD-1 blockade in this lymphoid malignancy. In independent pilot studies of two different PD-1 blocking agents, patients with multiply relapsed/refractory cHL experienced remarkable clinical responses that were often durable. In our competitive renewal application, we propose to build on these findings with the following specific aims: 1.0) Determine the relationship between PD-L1/PD-L2 alterations and outcome, response to PD-1 blockade and additional genetic bases of immune evasion in cHL; 2.0) Elucidate mechanisms of response and resistance to PD-1 blockade in cHL patients; 3.0) Develop a comprehensive approach to analyze genetic bases for immune evasion in cHL; and 4.0) Define the clinical activity of PD-1 blockade at earlier timepoints in the treatment of cHL. The proposed studies, will define complementary and/or confounding genetic bases of immune evasion and mechanisms of response and resistance to PD-1 blockade and inform our incorporation of PD-1 blockade into the standard therapy of cHL.